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Vol V, No. 1
THE THALATTOSAURIA
A ( T i; u I 1' () |- MARIN E R E 1' T 1 E E S ERG M
TU I A SS I (• () I' (' A E I EO l{ N I A
'J 1 1 E
Bv JOIIX (" MKKKEV.M
I>M Kh May '.I. r.iil.">
-^\X FKANCISCO
V V K l,T- II i: 1' V.\ I II I A ' A 11 I, M Y
C O ^I M I T T E E ON P U B L I G A T I O X
IjUVErktt Mills Loomis, Chainnan
Xi.vm-.vfi Kri.i, Joseph W. Hobsox
THE THALATTOSAURIA
A (ji-oui) of Marine Reptiles
FKOM THK
Triassic of ( 'alifoniia.
By
JOHN C. MERIUA.M.
('0NTENT8.
I'l.ATKs i-vrrr.
Introduction 8
Ordinal and Family ('HARAcrKus 5
Occurrence and Age 5
Materials Available 7
(Ienehal Skeletal STurcTCKE S
Skull ; 8
Facial Jiet/ion 8
Front o-parietal Region 10
Temporal Region 11
Qiiadrute, Suspensorinni 12
Orbital Region 12
Palatine Region lo
Mandilile 15
Dentition Id
(Inalliir 15
]'omerine 17
Pterygoid 18
Fv net ion 18
Vertol)i;u" 18
Ribs l!l
Trve Rihx li»
Alnhnninal Rihn li)
( 1 ) May •">, 1»).
Ml
Z ('ALIFt)]!>MA ACAIUOIV OF SCIKXCKS
Linil)S and ( iirillcs 20
Pelvic Arrli initl I'lixtcriar Limh 20
Pectoral A irli 21
Anterior Limh 21
Habitat, L(k'cimhtiiin. I'don 22
Affixitiks 28
(_'oiu|>aris<m with Similar or Uclatril Types 28
IchthyoHit II rill 24
Par(t»uchia 2()
Sqiiamalit 27
Priiiiinhisii iiriii 28
( 'liorititoderii 28
Proteroituchvs 29
Priitorosini rill 29
h'li i/iirliiii'i'jitiiiliii 81
('(inrlusidiis 81
(iEXERIC AM) SpEiIFIC ( 'i 1 A K AiVkRIZATK INS 88
TlialattositiiriiK 88
Thdlnttoiiini riix iilcrniiil me 84
Mcasuii'iiieiits 84
Thitlnttoi<(iiiru>i nhasteiisis 85
Measurements 85
TliiiUilloaini riia perriiii 8(5
AVf'/().vv( )( ni.s- 8 (
Necfii.'<iiii riix li alius 88
INTRODUCTIOX.
Ill the course of the lirst investigation of the I'eptilian fauna of the
( 'aliforuiaii Triassic, the w ritei' exainiiieil a peculiar jaw with a differeiitiateil (h'li-
titioii which was exposed on a specimen loaned t<i him for study by rrofessor
James I'errin Smith. This dentition was seen to reseml)h' the tigures of
Mirnfiaurns puhlished hy E. Frass/ and in a preliminary note on tiie Ichthy-
osauria of the ( 'alifornian Triassic" it was referred to that genus. Later prepa-
ration i-eveale(l the presence of other parts of the skeleton and showed a strueture
different from that of any ichtliyosaurian. This form was therefore not included
among the Ichthyosauria described later from the ('alifornian Triassic.''
During tlie Held seasons of 1002 and 1903, expeditions from the University
of California carefully worked over the greater portion of the Triassic limestone
exposures in Shasta ( 'ounty, and made special efforts to secure material from
whieh a satisfactor\- determination of the aflfinities of the unknown form could
be made. As the result of this work, a large collection of ichtliyosaurian
material was brouglit together and with it a considerable number of specimens
representing the new group. The preparation of this material has in all eases
been diffieult and has necessarily proceeded slowly, l>ut it has resulted in giving
us a fair representation of the most important tdements of the sktdeton.
The acquisition of our knowledge of the Thalattosauria has been made
possible through the generous assistance of Miss A. M. .Mexander. who has not
only contribute(l the tinancial support of the field work, and in part also of the
preparation of the material for puldication, but was hers(df the discoverer of the
specimens which furnish the greater part of our knowle(lge of the fundamental
skeletal structure of the representatives of this grouj).
Acknowledgments for \aluable services in connection with this investiga-
tion are also due to all the members of the University of ('alifornia licdd parties
which have worked on the Triassic limestones. To Trofessor .lames Perrin
Smith I am under obligation for the informatioii which led to the lirst ex[)lora-
tion of the Shasta limestones in search of saurian remains, and for the loan of a
valual)le type specimen. To Mr. K. L. l'\irloiig 1 am especially indebted for
v<'rv efficient assistance e.xtt'iiding through every stage of the work, from the
collection of the specimens to the final preparation of the material for study.
I'r. T. \\ . Stanton has loaned nii important sjx'cimen for study and description.
1 E. Friiss, Ichthyosnurieid. deutschoii Trias & Jura Ablng., PI. in, figs. 1-4.
2 Science. !i. ser. v. 1.5, p. 411.
s See Triassic IchthyoptcrvKia. linll. I>ci>t. Ccnl. fiiiv. Calif, v. :J, no. 4, p. 8.'i. Dentition.
4 CALlKOItXIA ACADKMV l>F SCIKXCES
While pi-fpuring tliis report, sonie WH'eks were spent in examining. typical
specimens of forms in related groups. For favors in connection with the study
of such material, the writer would expi-ess his most sincere thanks to the follow-
ing gentlemen: Professor 8. W. Williston, Dr. \. Smitii Woodward, Dr. C. W.
Andrews, Dr. E. Frass, Dr. F. von Huene, I'rofessor E. Koken, Dr. Louis Dollo,
Professor Henry F. Oshorn, Dr. Lortet.
V)ii rcrxiiil (if CdJ ifoniHt .
Marrli, J! )().',.
Superorder DIAPTOSAURIA.
Onlci- THALATTOSAIHIA.'
Mariin' snuriaiis with a Khi'cvia t (■<! prdpodial a n d c [>i pod i a 1 liiiil)
segments, eloiigatcil facial rcuion, and nnMliaii cxtcrual narcs.
Slvull with superior and lateral temporal opeiiiiins and a pineal
foramen. I'revomers and pterygoids as well as jaw elements
dentigerous. General structure of skeleton of the rhynchoceph-
a 1 i a 11 t y [) e .
The group is eonnioseil of specialized natatory forms known only from
marine deposits. It stands in somewhat the same rcdation to the typical
Rhynohoeephalia as tliat which the Mosasauria hear to the Lacertilia.
Evidently derived from a primitive land or shore 1 )iaptosauriaii, it has taken
somewhat the same course in evolution as was foUoweil later hy the Mosasaurs.
Family TllA LATTUSAURIDAE."
Skull elongated, with slender rostrum. External iiares sepa-
rate and not far in front of the or hits. I'rema x i 11 a ries elongated
and forming a large portion of the snout. I'reni a x i 1 1 a ries, maxil-
laries an<l dentaries sculptured on external surface. Superior
and lateral temporal openings and pineal opening present.
I'revomers with two rows of heavy. low-croAvned teeth. Ptery-
goids with four or more rows of curved conical teeth. Prema \il laries
and anterior end of dentary with slender conical teeth. Posterior
part of dentary generally with de[)ressed or iiattened teeth.
Vertebrae amph icoel ous, neural spines generally high and
slender. Dorsal rihs single-headed. Abdominal riiis present.
Coracoid reniform, elongated a n t ero-posterior ly. Scapula narroAV.
Humerus short, expanded distally. Radius and ulna about half
the length of , the humerus; radius with median constriction;
posterior border of ulna convex, radial border concave.
OCCURRENCE AND AGE.
The material upon which the group descrilu'il in this paper has been
based was all obtained in exposures of the Hosselkus Limestone lying between
Squaw C'reek and Pitt River, in the northern part of Shasta County, California.
1 J. C. MeiTiam, Bull. Dept. Geol. Univ. Calif, v. :f, no. 21, p. -12U.
2 IbUi.
6 CALTFiil.'MA ACADKMY dl' SCIK.N'CKS
Sprciiiicus wrrc found at miiiicnius lucalitics in the cxtctisivc outci-oiis of this
linicstoni', hut the pi'inciiial concctioiis were UKuh' at localities known as Smith's
( 'ovc. Hear Cove, Grassy I'oint anil North Fork. The lii'st three localities are
all on I-Jroek Mountain, at tlie southern end of the belt of limestone nortli of the
l*itt. Smith's Cove' lies on the soutliwestern side of the ridge. Grassy I'oint' on
the northwestern side, and Fx'ar Cove'' near the middle of the eastern side.
North Kork^ is a locality on the north foi-k of S([uaw Ci'eek and ahout two miles
northwest of the Kelley Kancdi.
The l)ones occur in practically all horizons of the limestone, hut good
material is more common, or at least more easily obtaineil, in the softer, slightly
shah' hiN'crs widl e.xjiosed at the localities mentioned.
The limestone section has heen divided hy Professor James. Perrin Smith ■\
on the basis of faunal distribution, into the upper or Spiriferina beds, middle or
Juvavites beds and lower or Tratdiyceras Ijeds. The softer layers, where the best
specimens were obtaine(l, Ixdong in general to the lowei' oi" Trachyceras horizon.
In the other beds the material seems to be much more fragmentary and little
but loose bones or teeth was ol)tained.
in all eases the remains have been very tirndy united with the black
limestone matrix, and successful preparation was possible only with the aid of
an electric engine. As the bones are black, as well as the matrix, it was in
manv cases impossible to trace their outlines until they had been moistened with
hv<lrochloric acid and allowed to stand for some days. This treatment resulteil
in the appearance of a (hdicate blue tint in the bone, evidently due to the
pi'esence of the ndneral \'i\'ianite. making it possible to follow the lines of con-
tact with little difhculty.
.\ssociated with the thalattosaurian remains are numerous ichthyosaurian
bont's, a few selachian teeth, occasional ganoid scales, and great nund)ers of
molluscan slndls. There are also a few brachiopods, corals and echinoids. The
most c(nnmon of all forms are (he ce])halopods. which fre(|uently make up a
large pai't of the rock. In the moi'e shaly layers they may be replaced by the
lanudlibrantdi genus llahihin. \ list of the most characteristic genera would
incdude the following: vert(d)rates, — Shasfasaurus, Delphivosanrns, Tdrddoieniiix,
Merridniid, Ihjhdihix: in\'ertebrates, — Tropitcs, Sdfjeiiifcs. Kntdiiidccrdx, .hwdrifi's,
I'olycyrhi.'i. I'minicln/ccrds. Tirdlitcs, ArpadH('>^. Arcixlrx. Ortlmfcrds. Xunfihi.-!. Atrdctifcs,
Halobia, Rhynchonella, h^piriferina, Ciclarls.
1 Sec. 11 and 12, T. U N. It. 2 W, Mt. D. Mcrid.
2 Sw. 3."), T. 35 N, R. 2 W, Mt. 11. Mfrici.
3 Sec. :«, T. 3.5 N, R. 2 \V, Mt. I). Meriil.
4 Sec. 1, T. 3.T X. ami Sec. 3li, T. 'X, N', U. 2 \V, .Ml. I). Mciiil.
5 See Comparative Slratigraiihy of the Marine Trias of Western .\nieriea, I'roe. Calif, .\eail. Sei. M ser. lieoi, v. 1, no, 111,
[>. 300.
MKHIUA.M Till". TIIAI.ATTnsAlMMA /
The iiivcrt('l)nitc faunas have Ix'tMi extensively studied Ky Professor
Smith', and are referred 1)V him to the I'pper Triassic on the eviih^iee of general
striking simihiritv of thi' fauna to that of the Alpine Triassie of Europe, even in
some cases to the point of identity of speeies. Also in the ease of the lehthyo-
sauria, almost uncjuestionable evidence of late Triassic age is Liixcii in the stage
of evolution or specialization of various parts of the skeleton. In general this
is near the stage i-eacheil hy the hditliyosauria of the latei- Triassic of Italy.
This is particulai'lv noticealile in the structure of the lindis. girdles and
vertel)i-al arches.
The preseiKH' of innumi-rahle cephalopods with hracdiiopods and corals,
in a limestone containing for the most jiart hut little argillaceous material,
leaves no room for doul)t that the deposit was formed in a fairly (dear sea, into
whicli there was but little drainage at this point. The reptilian forms whicdi we
tind in these strata evidently Ixdonged to the typical marine fauna of tlu- late
Triassic.
MATEHIAbS AVAILAUI.E.
The specimen whiidi has furnished the most satisfactory information in
this investigation is the tvj)e of Tliahitfosdurus ukxcnidrae (No. ilOS;")). Excepting
the anterior part of the skull and portions of the limbs and girdles, the skeleton
had long been exposed and was larg(dy weathered away. The remaining part's
include the anterioi' two thirds of the skull with a small jiart of one temporal
region. Of the girdles and lindis there are present the scapula, coracoid,
humerus, ulna, three l)ones wiii(di represent the lower part of the pelvis and
possibly the fenuir, and some scattered ossicles which may be either carpals or
phalanges. ()f the vertebral column there are pai'ts of about thirty vi-rtebrae
extending in an interru})te<l series fi'om the hea<i to the anterior caudal region.
There are also nunu'rous scattered true ribs and abdominal ribs.
.\noth(M' specimen (Xo. '.)()S4 ), certainly of the same species, shows a por-
tion of the skull with good mandible and (juadrate, also both humeri, a radius
and several well preserved doi'sal vei'tebrae.
Two other smaller skulls having the same size and form ai'e also referre<l
to TJialaitosaarm but probably do not Ixdong to the type species. ( )ne of them
(7^. sliastensis. No. 1)120) shows the innei- side of the j)osterior half of a skidl in
good state of preservation. With it are several good vertebrae, limb bones, ribs,
abdominal ribs and teeth. In the second specimen the ]iosterior three
fourths of the skull are present, fairly preserveil but very difficult of preparation.
1 Lor. fit.
8
CAI.IFUKMA ACADK.MY dl' SCI l'..N( 'KS
A fourtli skull, t lie type of 7: iicrriiii , sIkiws the iiivatcr part of the inaiidihU',
maxillary ami palatine, with poilioiis of miiiu'roiis other elements of the skull.
The type of the ^enus Xcrtumnrns consists of the posterior two thirds of a
niandihli' with the frontals, parietals, a prefontal, a post-fronto-orbital and part
of a (|uadrate. Several loose jaws, portions of skulls, vertebrae, ribs, etc. are
also I'eferi'ed to this u'enns.
GENERA b SKELETAL STRUCTURE.
Skull.
I'l.ATES I-VI.
Considerable p)arts of tin- head are shown in live speeimens. In all of
this material, excejjting the type of 'rhahitlo.mKrits, the skulls are small and the
bones thin and diflfieult to prepare.
The skull in the type specimen was fortunately broken into four segments
by wide vein-Hlled cracks. In pi'eparation, tlu'se segments were separated so as
to show all sides of the bones and the cross-sections of the skull. The sections
have been of espec-ial value, serving as checks in observations on the position
and arrangement of the bones.
The restorations of the skull (Text tigs. 1 and 2, and 1*1. vi) were leased on
the type specimen. The temj)oral and fronto-parietal regions and a portion of
the mandibk' are restored from T. xliasteii-'^i.'i.
Fig. 1. TJuilaltiixamns ((luKndrni'. Kccniistnu-tril sUull, lateral view, X ^g. Tin, pixMuaxillarv ;
.1/, maxillary ; -V, nasal; 7:.', siipfrinr naivs ; /•', frniital ; /'i-, iiarirtal ; /'/', pi't'l'i'diital ; /V", i"ist-fr(iiitii-(ri-liital ;
J, jugal ; X, lachrviiial ; /'?, palatim' ; iSc, sclcrntir riii>.'; N/, si|uaiiiiisal ; 'i', (nunlrati/ ; . I/-, articular ; N'l, supra-
angulav; ,1//, angular ; T^, dentary.
Facial Rcj/idii. — As is shown in J'late i, the facial region of this skull is very
slender. The snout was narrow, exhibiting some resend>lance to that of the
long-headed Mosasaurs.
MKi;i;i AM — Till-: tiia i, \ rn is. \ri;i a 9
( )v('i' a laruc part of the external surface of both niaxiUaries ami [ireinaxil-
laries, tlie rostral re<iioii has sciilpfiiri'il into it a series of pits ami ui'ooves. They
run lon_i;'itu<liiially on the jireinaxillaries hut have in iicnera] a radial arrange-
ment on the maxillaries. They a})pear also on the anterior portion of the lower
jaw. While not so strongly impressed as in the ('rocodilia or Stegocephalia they
are nevertheless a eharaeteristic feature of the skull in this gi-oup.
The superior iKin'iil ajxun'tti/ii wvYv situate(l only a short distance in front of
the orl)its and are almost immediately ahove the inferior openings. They are
separateil l)y a heavy har consisting of the nasals, frontals and premaxillaries.
The superior openings are hounded on tlie external side liy the nasals, the pre-
maxillaries and apparently to a slight extent hv the maxillaries. Anteriorly
they are eloseil hy the premaxillaries. In the type of TJialnttdsaurns there are
also present eertain peculiar elements which have somewhat the appearance of
anterior prolongations of the prefrontals rising along the anterior margins of the
openings. The character of these elements is, however, somewhat doulitful.
The greater portion of the snout is formed hy thi' pre niaxiUaries, which extend
back to form part of the boundaries of the narial openings. The needle-like
posterior ends reach hack of the nasals and are thrust between the median ante-
rior prolongations of the frontals. In the cross-sections (PI. ii, figs, la, 16 and
Ic) the })remaxillaries are seen to be distinctly separated. At section c (PI. ii,
fig. Ic) each element shows two large dependent branches, one of which f(_)i'ms
the external lateral wall of the snout, the other resting between upward pro-
longations of the prevomers. The alveolar margin is set with conical, slightly
recurved teeth. The extreme anterior end of the premaxillarv is not known,
but judging from the extent to which this bone has narrowed anteriorly, as also
from the character of the nearly perfect termination of the lower jaw, only a
very small fragment is missing from the type specimen. The dentigerous por-
tion of the premaxillarv seems almost to have equaled that of the maxillary
in length, though the inferior margin of the maxillary is longer.
In T. aJe.ra inlnif the posterior end of the inaxiUary is considerably expanded
vertically, reaching upward to the lateral prong of the frontal, with which it is
folded into the prefrontal (Sec. a. PI. i, fig. 1 and PI. ii, tig. la). The posterior
])art of the alveolar margin is not well preserved an<l it is not known whether it
boi-e teeth. No part of this boi-der appears to Ite pitteil or grooved for the
reception of teeth. ( )n the antei'ior portion there are two promiiiences which
seem to represent fangs from which the crowns have been almost entirely
removed.
In T. pcrri III {\\r maxillary dentition is very well shown excepting on the
posterior portion of the jaw, which seems to have been edentulous. The teeth
are sharply conical and are set in dee[>, distinct |iits.
10
<'AT>IK(>i;XlA ACADK.MV OF S('IF,.\( 'KS
Tlie iKisals are clearly shown in the type of Thdldftnsdtinis. They are not
large and horder mainly the median and posterior sides of the superior mires.
They do not meet medially but are separated by the frontals and premaxillaries.
The posterior ends rest between the forks of the frontals. A tendency toward
separation of the nasals by extension of the frontals and premaxillarit's is seen
in many reptilian skulls, particularly in rhynchocephalian, lacertilian and sauro-
pterygian forms, but such t'omplete sepai'ation as is shown here is so rare that
it may be considered an important character. The neai'est approach to this
structure is seen in the Sauropterygia.
In that group the nares are situated close to the orbits and are either
median or sul)tei'minal. in all cases the premaxillaries foi-m a large share of
the snout. In the Nothosaurs the nasals have almost the same form as in
Thalattosmiriis, and the premaxillaries are thrust back between the nares though
not in contact with the frontals. In Pisfd.^aiiru.'^ the premaxillaries touch the
frontals, separating the nares and the small nasals. In Plesiosaurns the pre-
maxillaries ai'e in broad contact with the frontals. in /hilichorln/iichojis, vavvntly
described by VVilliston. the premaxillaries extend hack to the parietals, sepa-
rating even the frontals.
Fig. '2. TlialdlldsadriiK iiU:iiui(lriii'. Kci'inistnictcil sUull, sn|i('rii>v view, X ^r. /')/(. |ireiiiaxillary ;
.1/, maxillary; .V, nasal; ]C, .«uinTiiir nares; /', t'rcnital; /'/■, i>ariftal; I'li. iiincal fnranii'ii: /'/', iirt'fnintal ;
P(o, liost-friintd-iirbital ; ./, jnijal; 7^, laclii'vnial ; /'/, jialatine ; N(/, si|nani(isal ; 't'. i|uaili'atr.
Froiito-parietuI Region. — This region is particularly well shown in the speci-
men of 'riidUtttnmnrus represented in Plate iii. Both frontals and parietals are
distinctly i)aii'e(l and on both the superior surface is nearly smooth, being
marked only by Hne lines and pits. The /Ve;/^//.s- are relatively large. Their
postero-external angles reach far back and partly clasp the anterior ends of the
parietals. Tlu' anterior ends are deeply incised for the reception of the nasals.
The median anterior forks extend forward as far as the middle of the superior
nares, while the lateral forks reach almost if not (piite to the outer border of
the nares.
.MKKKIAM Tin: Til A I, ATTOSA UKl A 11
The ixtrictuls art- iiiurli smaller than the t'ruiitals ami an- also scjuirated i)y a
miMliaii suture. A large parietal foramen lies between the two elements, hut is
a considerable distance behind the coronal suture. The posterioi- outei- angles
of the parietals are produced backward around the outer side of the superior
temporal openings for more than half the length of the upper temporal arch.
In tigui'e 2a, Plate i\', what appears to be the squamosal is seen to reach
forward over the post-fronto-orbital to touch the frontal. If this is the normal
relation of these (di'ments, the outer border of the parietal is separated from the
post-fronto-orbital. The median portion of the parietal is also })roduced back-
ward as a slender arm and was probably in contact with the squamosal. The
two posterior arms seem almost to have surrounded the upper temporal opening,
giving to the skull an altogt'ther peculiar character in this region.
Tcinporal Reginu. — The skulls appear to be characterized by the presence of
both superior and lateral temporal openings. The ■mperior openings are con-
siderablv smaller than the lateral. .ludgingfrom the specimen seen in I'late iii,
the posterior ends of the pai'ietals wei'e very slender and were dropped some
distance bcdow the level of the roof of the skull, so that the superior oj)enings
faced backward somewhat, as in Belodaii. The anterioi- half or two thirds of this
opening was enclosed by the parietal. The posterior boundaries have not been
seen. They were probably formed by connection of the parietal and squamosal,
though the supraoccipital may have intervened as seems to have been the case
in SdH ra iindiDi.
The rehitivtdy large hilcral fi'iiijionil iipoiiiKji^ are seen in two specimens
(IM. Ill, tig. 2 and 1*1. iv, tig. 'l(i). The boundaries are not perfect, even in the
more nearly complete specimens, owing to the absence of the quadratojugal. In
both instances, however, the jugal sends backward a long and strong process
extending more than half the distance to the ([uadrate, and in one specimen the
posterior end of this process is roughened as if fi'om contact with a (juailrato-
jugal. Under these circumstances it would lie ditHcult to believe that the
iiifcriar liar was incomplete. Should we assume that it was not coin])lete it would
l)e necessary to supfiose that it is caught, as it were, in thi' process of breaking
down, as no form losing the lower i)ar retains a posterior jugal process similar
to that shown here, lii reality there is hardly reason for supposing that the
lower bar was even weak, as the posterior process sent out from the jugal is not
stronger than it is here in many forms in which this arch is t-onsidcred w(dl
developed.
The iipjX'r fciiipiirdl Ixir is certainly made u]) to a gi'eat extent (.)f the large
post-fronto-orbital and the s(Hiamosal. as seen in IMate IV. ligure 2(i. with the
addition of the outer posterior pi'ocess of the parietal lying on the me(lian side
12 CAI.IKoliXlA ACADK.AIY ( H' SCIKXCKS
of tlie bar. Even on tlie most coiuplete spcriuuMis (I'ls. in and iv) it has been
impossible to determine certainly whether a prosquamosal is present or not, as
the character of the bone is sucli that the sntnres immediately above the
quadrate are very difficult to determine. On what is taken to be the quadrate
in a frafiinent of the temporal retiion of the type of TliakiftosaKrii.-^ (1*1. ii, fig. 4)
there rests a downwardly' projecting arm which appears to be a part of an ele-
ment that belonged to the lower side of the upper temporal bar. Evidentlv it
extended down the outer wing of tlie (|uadrate, almost if not quite to the
quadratojugal. The inner side of this bone, as also of that resting on the
summit of the (juadrate, is weathered away and it is not impossible that they
were originally connected. If united, the squamosal must have had a form
somewhat similar to tliat of SjiliciKxhui. If separated, the lower (dement is
apparently a discrete prosquamosal.
Quadrate, Suspensoriam. — The (jnadrate is well shown in position in one
specimen (PI. in, fig. 2) and macerated out, though associated with the posterior
end of the mandible and the cranium, in another (PI. ii, tigs. 2a and 2b). It is of
distinctly rhynchocephalian ty{)e, though approaching the laccrtilian form in
the development of a stronger posterior hook and a broad exterior wing. While
the posterior side of the distal end is rounded upward the anterior side is dis-
tinctly flattened as if from contact with a quadratojugal. The presence of a
high extero-laternl wing seems to precdude the possibility of there having been a
fenestra between the quadrate and (luadratojugal, as in the typical Rhynchoceph-
alia, thovigh there may have been a small opening near the distal end.
The relation of the quadrate to the temporal bones is such that it must have
been immoval)le, in contrast to the general relations in the Squamata.
Orhitdl H('!/iini. — Tlu' specinu'ns of 'rhdldftdsaiiriis show portions of large
sclerotic plaf(.'< in the orbits. They are similar in form to those seen, in the
Mosasaurs. In at least one instance a plate is deeply grooved on the margin, as
occurs in forms in which the sclerotic ring is particularly heav}' and strong.
In the boundaries of the upper side of the orbit the prefrontal and post-
fronto-orbital come so close together that the frontal hardly appears on the rim
of the orbit. The posterior boundary is formed by the heavy ascending process
of the jngal, and a single uj)per element evidently representing both the post-
frontal and the postorbital. No evidence has been obtainecl which would tend
to indicate the existence of a separate jiostfrontal resting al)ove this bone. The
apparent contact of the squamosal with the frontal might be interpreted to mean
that a greatly reduced postfrontal is fusecl Avith the anterior arm of the squa-
mosal, but until we have more definite proof of this it can be considered only as
a mere possibility.
MKIv'KIAM TllK THALATTOSAl'IUA 13
'r\w pirfniiita/s arc lari;c robust elements extending t'nini the middle of the
upper boundary of the orl)it forward along tlu' inner side of the maxillary.
The small hii'linjiiKtl, extending over only a limited area of the face, is well
shown in the tvi)e of 'riidlnttomnrus (PL i, tig. 1, L). The laehrynuil foramen is
also distinctly seen here. In cross-section /), Plate n, ligure 16, .1 there is seen a
peculiar element apparently distinct from the nasals, maxillaries, premaxillaries
and prt'vomer. If suidi is I'eally the ease, this is prohahly an anterior j)rolongation
of the })refrontal. This would, however, rec^uire an extraordinary enlargement
of the anterior end of this hone, and further evidence is i-e(|uired before its
relations can be satisfactorily (letermine(l.
Palatine Region. — It is in the palatine region that some of the most dis-
tinctive characters are seen in the nieiidiers of this grou[i. The general aspect
here is of a primitive form in which the rostral region, and in it pai'ticularly the
vomerine dentition, exhibits distinctive specialization.
The position and relations of the jiretWHer are iiest shown in the type of
Thalattosaurus (Tl. i. tig. 2 and PI. ii, tigs. V> and Ir). It is here seen to lie
largely between the maxillaries although reaching far foi'ward along the rostrum.
It is much elongated antero-posteriorly and has in general a sphenoidal form.
So far as can be determined from the sections no median suture is present,
though the structure niav have been })aired. From the meilian portion of the
posterior end three laniiinie project backward, the meilian plate being much
smaller than the others. ()u either side of these laminae the posterior margin
slimvs a regularly roun(le<l excavation, representing the anterior borders of the
inferior nasal openings. The posterior plates evidently connected the prevomer
with the palatines or the pterygoids. The palatal surface of the prevomer
bears two long rows of teeth following the lateral margins. Posteriorly they
are separated by quite a distance, but they approach each other near the middle
of the l)one and run paralhd from that point forward.
In another specimen ( I'l. v, Hgs. '2(t and 21)), which was found separated from
other skeletal remains, exactly the same foi'm is shown. In the type of T. perrini
( IM. V, tig. o) a part of a prevomer of the same general form is known. Fragments
of several other sjiecimens have been found to show corresjionding structure. On
all the specimens in whi(di the antcrioi' end of the prevomer is shown, the dentig-
erous portion of the bone is seen to bend downward sbari)ly in the middle.
In the specimen which was entirely separated from other bones of the cranium
(PL V, figs. 2a and 26), the drop is very pronounced and cannot be fully accounted
for by distortion. A similar but less prominent lieiid is set'u in the prevomer
of 7'. iierriiii. Evidentl\- the middle poi-tioii of the prevomer was produced
downward somewhat, making the tooth row convex. The downward sweep is,
14 (^A,LIK(li;.\'lA ACADK.M Y OK SCI K.NCKS
lu)wevov, very pronounced and must have carricil the vomerine teetli down to
meet tlie low posterior teeth of the mandihulai' series.
Tlie foi'm of the pi'evomer seen here suii'iicsts tlie Khynehoeephalia, hut
differs fi'om the known types in tlie character of the (h'utition. The hi'oa(h'ned
teeth of the posterior portion of the hone liad possil)ly a function somewhat
simihir to that of the smaHer vomerine teeth of the Choristodera; hut they were
much less numerous, were much larger, and were confined to the lateral margins
of the palatal surface.
The inferior narial openings in ThalaUosanrtis are large and are situated
almost immediately l)elow the superior openings, the anterior horders being
slightly anterior to the posterior borders of the upper openings. The external
borders are formed in part hy the ma.xillaries, as the anterior ends of the j)alatines
d(j not appear to come in contact with the ])revonier here in the manner in
which they do in the ('horistodera.
The anterior ends of the palatirt.es are turned upward i)ehind the nai'ial
openings and art' deeply grooved to form the posterior walls of the nasal pas-
sages. As seen in section a (IM. ii, lig. la) the external hoi'dcr of the palatine is
enfolded by the thin posterior end of the maxillary. In 7'. pcrriiii (IM. iv, tig. '.\)
the same relations are seen, only tlie narial opening is smaller. The median
border of the palatine swings far around the nares here as if it had probably
joined the prevomer hi'oa<lly. The relations of the posterior and median sides
of the palatine are only imperfectly known. The groove on the median si<le of
the element (PI. iv, tig. ;>) is not such a contact as Avould occiu' if the correspond-
ing element from the other side were met here. The presumption is that the
anterior end of the pterygoid passing along the median l^ordi-r of the palatine
was in contact with this surface.
In none of the skulls examined have there l)een found any indications of
the existence of teeth on the palatine. In two specimens (PI. in, fig. ."! and
PI. IV, fig. 3) this element can be seen in place and has been followed backward
for a considerable distance without showing any traces of teeth, though they are
well shown on other elements. The teeth shown close to the palatine on Plate iv,
figure •"> are entirely distinct from it. They prol)al)ly belonged to the ptervgoiil.
One of the most remarkable features of the type specimen of ThalaftomiirKs
is a peculiar dentigerous bone which lay below the palatine region and above
the separated rami of the mandible, ('onsidering the position of the specimen.
the character of the material, and the fact that no bones of other animals have
been found in the matrix, there can he no reasonal)le doubt that it belongs to
this skull. 'Hiis hone (JM. v, iigs. Ir;, ll> and Ic) is held to he the pteryf/oid. It
consists of a narrow, thick plate, one border of which boi'e five rows of teeth. The
MKIMMA.M TlIK Til A I,ATT< ISA T i; I A 15
!^
Opposite iiiar.iiiii of tlic plate supports a lii^li. tliin, ti-iaii^ular wiiii;- standing
almost parallel witli the tootli-heariiig sui-faee. Tlie surfaee of this wiiig is marked
on one side hv I'adiating sculpture sotnewliat like that of the maxillary, except-
ing that it is larg(dy in ndief. The at'ute end of the wing is drawn out to a ver}'
thin edge. The hroad end is eonsiderahly thicker and shows a deep groove
wliere it was prohahly in contact with the (piadrate.
The j)f<T)/i/iiitl fctili are in four rows with alveoli for a hfth. I'nfortunately
the crowns of nearly all wei-e hroken oi- weatliercMl off and only the w^ell preserved
fangs remain. The tei'th are all set in distinct pits and are inclined sliarply
toward the thi(d<ene(| enil of the hone.
Considering that the palatine is <'dentulous and the vomerine teeth have
speciali/,e(l toward the low, hr^ad type present only in a single row on eacdi side,
it is rather remarkahle that the pterygoid teeth should he so numerous and
evidentlv of the recurveil. conical tyj)e. There is, however, no apparent escape
from the conclusion that sucdi is the case. Apparently the vomerine teeth
serveil largelv as crushers, while the iiterygoid teeth assisted deglutition. The
type of pterygoid represente(l here does not correspond exactly to an}^ that has
so far come to the writer's notice, hut is not far removed from the type seen in
some Kliynchocephalians.
In one specimen of T. slidstensis (PI. iii, fig. '2., Kp) thei'c appears to he a frag-
ment of an epipterygoiil in its natural position al,)o\'e the pterygoid. No ecto-
ptei'ygoid has heen recognized.
Mainlihie. — (I'Is. r, iii and iv). Though no single specimen shows the whole
of the lower jaw. overlap])ing portions of several exhibit the whole structure of
both the iniiei- and outer sides. The jaw is characterized hy the sculpturing of
the dentary, as shown in the type of Tlialaito-^ditrKs, hy the length of the angular,
and by the promincMU'c of the coronoid pr<K"ess.
The deiifary does not appear to form the lower burdei- of the outer side of
the jaw exce{)ting along the most anterior portion, owing to the extreme forward
extension of the anguliir. The connection of the ranu at the symphysis was
loose and they have fallen awav from each othei' in all of the specimens examined.
In Thaldtfdsdiirtis the ti'cth u])on the dentary extend back almost to the
extreme jxjsterior end of that bone, where they are low down on the inner side of
the jaw. Th(\\' are either set in depi'essions or appear to be fuseil to the jaw.
The extreme posterior end of the jaw is forme(l by the articular, which
extends forward to be covered anteriorly by the splenial. The supra-angular is
large and makes up the greater part of the posterior half of the jaw. The
angular also forms a considerable part of the outer side of the jaw and ranges
forward well toward the antei'ioi- end of the ramus. A large splenial covers
li) CALIKOIJMA ACADIOIV OK S<TKN('KS
;i coiisidcraltlc part of tlic iiiiicr side of the jaw. It oxtondis bark to a point below
tlic middle of the coronoid and may reach forward almost, if not quite, to the
symphysis.
The most characteristic feature of the mandible is the form of the coronoid.
This (dement is broadly expanded over the inner side of the ramus and reaches
with its upper border high above the supra-angular as a coronoid projection.
The form of tlie coi'onoid is strongly suggestive of the Lacertilia. though it is
approached in the true lihynchocephalia. Particulai'ly is tliis noticeable in
the jaw of Necf(imi(rH<!, wliicli taken tiy itself would appear unquestionably
lacertilian.
I>ciitition.
The dentition is well shown in the tyite specimens of ThaJattosavrus, as also
in the lower jaw of the type of Necfomnrun, and more or less imperfectly in most
of the other specimens. In addition to the jaw elements, the pterygoid and
prevouier are (U'litigerous while the palatines are not known to have carried teeth.
Teetli oftheJav's. — The liisrrtioit of the teeth on the ui)])er and lower jaws
varies considerably within the group. In ThalnHdmurus the teeth of both upper
and lower jaws seem to rest in pits, which may be in elevated bases formed by
the alveolar margin. In some cases they appear to be fused Avith the jaw bone.
In T. perritii the teeth of both jaws rest in distinct pits. The depth of the pit
and the general character of the insertion are to a considerable extent dependent
on the form of the crown. The slender conical, anterior teeth are very deej)ly
set in the jaws, while the pits for the low, broad-crowned, posterior mandibular
teeth are much shallower. This may have been the case in T. xlexaudrae also,
but the preservation of the anterior portion of tlu' jaw (jf the type specimen has
not ])ermitted a satisfactory investigation of the insertion.
One of the diagnostic features of Thahittosaurm is found in the remarkable
differentiatiDU of the mandil)ular <lentition. In T. alexandrae (IM. i, tig. 3) the
crowns of the anterior teeth are slender conical with a slight lateral compression,
while the most posterior teeth are very broad and nearly Hat-crowned, resembling
considerably the form of the teeth of Phtcndns, although very much smaller.
The teeth in the middle portion of the jaAv grade from the Hat form to slender
conical, through the gradual development of a tubercle on the antero-external
portion of the croAvn. This elevation increases in size until it comprises the
whole crown. Unfortunately the dentition of the upper jaws is not well known
except on the anterior portion, where the crowns are conical as on the
opposing portion of the mandible. Ujxm the maxillary, portions of two or three
fangs are seen, but the crowns have lieen destroyed.
.\IF,i;i;lA.M TIIK. TllALATTiiSAriMA 17
In T. perriril (V\. iv. tiir. '■'>) the (Iciititiuii df the luwi-r jaw shows ayain the
foiiit-al anterior teeth with hiterally eoMii)ressed, low-crowiicd posterior teeth.
The depression in tlie hitter is, liowever, very niucii less than in T. alc.randrae.
Tn the upper jaw all of the teetli are eouieal. There do not appear to he any
low-erowned or laterally compressed maxillary teeth. The most posterior
[lortion of the maxillary was apparently I'drutulous ami it is evident that
the posterior vomerine teeth were in contact with the posterior portion of
the mandihular dentition.
Jn the type of TltalaftoMtiiriis the perfectly })resi'i-ved ti|) of the crown of an
anterior mandihular tooth shows very faint wrinkles in the enamel. ( )n the
dej)ressed pcisterior teeth the wrinkling of the enamel is more pronounced and
in some instances a faint tul)erculation is visihle. A single loose tooth found
with tlie jaws of this specimen has an elongated, somewhat compressed crown
covered with numerous strong longitudinal striae.
Associated with the head hones of T. shafitensis are several loose teetli show-
ins the form verv distinctlv. In all of these the crowns are conical, hut thev
vary considerahly in length and thickness. The slender, curved teeth (IT. iv,
fig. '2h) are prohaldy from the anterior portion of the jaws, and the shorter,
heavier ones (Fl. iv, fig. 'Ic) from the middle region. The ci'owns are all sup-
ported on heavy fangs, such as are present in teeth inserted in pits. The enamel
is marked with numerous tine, longitudinal Avrinkles or striae somewhat finer
than those on the corresponding teetli of T. akxandriw.
In no case has anv evidence been ohtained which would tend to show that
the l>ases of the teeth have a foldeil internal sti'ucture as in the Ichthyosauria
and (Tioristodera.
Vomerine Teeth. — In all specimens, so far as is known, v<mierine teeth are
present in only two rows, which are set upon the outer edges of the prevomer
instead of next the median line. The rows converge anteriorly and near the
middle of the prevomer they ai-e very close together. From this point forward
they run approximately parallel. In the postt'rior. diverging portions of the
rows the crowns are very low and roughly triangulai' in cross-section. In tlie
parallel portions the crowns are slightly higher. A \-ei-y sti'iking featui-e of the
\'omei'ine dentition is the downward sweep which it takes, the lowest jjoint
of the curve being at the place of convergence of the tooth rows. The teeth in
this region seem to have come in contact with the low-crowned teeth near the
middle of the lower jaw. The [>osterior vomerine teeth e\idently met the pos-
terior teeth of the nnindii)le.
The vomerine teeth are set in depressions and where seen in a cross-section of
the j)revomer (Fl. ii, fig. Ic) they ai'e known to extend a considerable distance into
( 2 j May G, 19«j.
18 ('A]JFOi;>-IA ACADEMY OF 8('lKiN'CES
tlic lione. The enamel is oniamented witli a lari;e number of line wrinkles
radiating' from the apex of the erown.
Pterygoid Dentition. — Closely set teeth were present in at least five rows on the
heavy median plate of the pterygoid. They are of slender conical form and each
is set in a distinct pit of considerable depth. Unfortunately the crowns have
not been well preserved. They are all nearly circuhir in cross-section and the
enamel seems to have been slightly wrinkled toward tiie base.
Finirtion. — The dentition of the Thalattosaurs is evidently tliat of swiftly
swimming fi>rms feeding in a large measure upon fish. The character of the
posterior mandibular and vomerine teeth of Tli<il(iif(i.'<(iiir>i><, indicating a crushing
function, probably means that this type fed also in })art u}>on some creature
with a shell which could be easily crushed. Such forms Avould have been found
in the numberless cephalopods of this epoch, and they doubtless furnished a
portion of the food of the Thalattosaurs.
A'ertcbrae.
ri.ATlO VII, FlOS. l-."!.
In the type specimen of ThalaUosaurus alexaudrae parts of over thirty verte-
brae are shown. They represent the cervical, dorsal and anterior caudal regions.
A number of loose vertebrae in a fair state of preservation are associated with
other specimens.
In Tliahiftosanrvs the centra of the anterior dorsals (PL vii, figs. 1 and 2) are
nearly circular in vertical, transverse cross-section. The anterior and posterior
faces are concave but not so deeply excavated as in the Ichthyosauria, the wall
betwet'n the two faces representing more than half of the antero-posterior diam-
eter of the centrum. The upper arches are rather slender and are not greatly
thickened. Tlie anterior margins are sharp. The posterior edges seem to be
blunted or rounded. Strong zygapophyses are present. A characteristic feature
of these vertebrae seems to be found in the closer attachment of the upper arches
to the centra than we find in the Ichthyosauria. In this respect they resemble
the vertebrae of the ]*lesiosaurs and (-rocodiles.
An upper arch of T. shastensis (PI. vii, tig. 4) shows the structure of the
neurocentra better than in any other specimen. The spine is wider antero-
posteriorly and is not so high as in T. akxandrae. Possibly this is due in this
case to the arch having occupied a more anterior position than the arch of
alexandfrae figured (PL vii, fig. 1). The zygapophyses are large and strong and
the facets well separated.
Tlie ribs of TJialaffosaitrus articulate on a single wide apoj)liysis, the upper
port ion (diapophysial) of which is situated above tlie middle of tlie ceiiti'um.
MKi;l;lAM TIIK THALATTdSAriMA 19
The surface of artirulation is coiisideralily iiarrowcil in the iiiiddU' Imt the apoi)h-
vsis is not seen to divide into distinet di- and i)ar- apopliyses. In the dorsal
vertchrae examined, the uppermost portion of tlic ril) head lias heen in articu-
lation with the hase of the neural arch.
In the caudals of Thaluttofianru.i (IM. vii, i\<j,. '■',) the centra are somewhat
angular in cross-section, though not greatly flattened laterally. The uppei- arches
are very slender and relatively thick. Large and [ironunent zygapophyses are
present. The faces are sharply separated and almost vertical in position. A slight
elevation of the neural spines may indicate a little l)roadening of the tail. The
structure of the vertebrae seems to indicate that the tail of T ha I aitosaurus was not
a highly specialized sculling organ as in the Ichthyosauria and the Thalatto-
suchia. The propelling function may have been performed largely by the limbs
as in the Plesiosauria. Evidence pointing in this direction is furnished by the
bones of the pelvic arch, which are relatively large and robust for a swimming
animal of this size.
Ril.s.
I^i.ATu VI r. Figs. 6 and 7.
True Riha. — Many fragments of ribs are present in the type specimen. In
these the shaft is apparently about as heavy as in 'the lehthyosaurs. The
middle of the shaft is grooveil on one side, the distal end is round in cross-
section. In the single specimen in which the liead is preserved but one articu-
lar surface is seen. In a specimen of 2. sJiasfensis showing several rib fragments
associated with the bones of tiie head and the pectoral arch (PI. vii, fig. 7) the
shaft is ratliei- heavv, is groove(l anteriorly, and there is a single wide articular
face as in Shasfasaurus.
In the dorsal region the rib heads have articulated largely on the broad
ai)ophyses on the centra of the \-ertel)ra, but the uppermost portion rested also
in })art against the base of the upper arch.
Alxloiiiiital Ribs. — ( »n one specimen (No. 9120) numerous abdonunal ribs
are present. They are long, and compared with the dorsal ribs are exceedingly
delicate and slender. It has not been possible to distinguish between median
and lateral pieces.
In the tvpe specimen the lower j)ortion of the skeleton with the abdominal
ribs had been largely destroyed, Imt a single fragment ap[)arently representing
an alidominal rib is seen between the distal ends of the dorsal ribs.
20 CALIFORA'IA ACAItK.MY oF SCIENCES
Limbs and Ciirdles.
Plate VII, Fui.s. IS, il and 10; Plate V[II.
The pectoral and pelvic arclies are both represented in the type specimen of
Thalatfomiirits. A])parently neither arch has been moved very far from its
original position with reference to the remainder of the skeleton.
Pelvic ^ircli (I ml Posterior LI nif>. — In the pelvic regioM of the type specimen
there are parts of several l)ones evidently re[)resenting a portion of the pelvis and
probably some of the elements of a hind limb. Only two of these l)ones are
complete enough to permit identification. Corresponding to one of them there
are in tlie collections two much better specimens (1*1. vii, figs. 8 and 10) giving
a fair idea of its form. This element is larger than the other and differs from
it somewhat in form. It exhibits characters which are not particularly definite
and might permit its identification as either of the inferior elements of the
pelvic arch or possibly as the femur. It is narrowed somewhat below the })roxi-
nial i^^nd or head and is considerably broadened distally. The expanded anterior
margin of the distal end is thin and slightly decurved. The distal portion is
thickened, excepting in the middle of the end, and is excavated along the distal
border. The proximal end is also excavated. On the more strongly concave
side of the neck there is a small foramen in all three specimens.
This element shows some resemblance to a femur, and when first examined
was thought to represent that element. It also resembles the pubis in the form
of both ends, in the curvature of the shaft, and in the twist of the outer margin.
The small foramen near the proximal end might o<'cur behind a trochanteric
elevation of a femur or in the pubis. If this is the femur it represents a type
of extremity quite different from that seen in the anterior lind), the distal end
being turned sharply backward and slightly U})ward. Propodial elements of
this kind nw not uncommon in natatory reptiles, but wiien pi'esiMit in the hind
lind). the fore limb is usually, though not always, of a simihir character.
Tlie other element belonging in this region (PI. vii, tig. 0) is again of some-
what indefinite form. It is quite similar to the first mentioned element but is
smaller and shows a greater expansion of the median ])ortion, producing a
prominent wing. This bone might l)e either pubis or ischium but is probably
the latter.
A fragment of another large element lying next the ischium may represent
the ilium or the femur. It is nearly straight and appears to be almost circular
in cross-section.
However we may interpret the elements which have been discusser!, it is
evident that at least one of them must belong in the inferior poi'tion of the
MKl;i;iAM THK THAI.ATTdSAriil A
21
pelvis, and that the characters of either or l)oth of them are such as to show-
that the pelvis was not of the i>late-like form usually seen in the primitive
Diaptosauria.
Both of the elements (lescril)e(l from the pelvic rei-ion of the type specimen
are large comi)are(l with the coi-aeoid, sea}iula and humerus. No matter how
we interpret them, they show that the posterior lind)s were possibly more
powerful than the anterior, reminding us of tlie peculiarly s[)eciali/,e(l Thalatto-
suehia of Frass.
Pectoral Arch. — The ]>ectoral girdle is represented hy the eoracoid and
scapula. No clavicle or intertdavicle has as yet been discovered. Several
fragments of large l)ones associated with the jx'ctoral
girdle mav represent one or hotli of these elements.
The eoracoid (PI. viu, fig. 1) is reniforni and has some-
what the form of the eoracoid in the ichthyosaurian
genus Merria)ina from the same horizon. It is, how-
ever, more distinctly reniforni, having a sliarply conca\-e
exterior margin.
The scapula (I'l. viii. Hgs. 2 and ;>) is comparatively
narrow reseml)ling that of the ( "roeodilians, Farasuchi-
ans, the later Ichthyosaurs, and most of the rhyncho-
cephalian forms. It differs from that of the Triassic
hdithvosaui's in lacking the considerahle distal expan-
sion.
The structure of the pectoral arch, so fai' as
known, seems more primiti\'e than that of the Ti'iassic
Ichthvo.saurs and is of distinctiv rhvnehocephalian tvi)e. ^V^ '^^ Jl"^^''ttom,'ru. ale,-
• ' . ^ 'I iiiulrne. A portion ol the n>:lit
Anterior Limb. — Elements belonging to the anterior |„.,toial arch and limb seen
limbs are found in the type and in two other specimens.
In the tvt)e the humerus and tlu' ulna are present. In
another specimen both the humeri are widl preserved
and with them is, a nearly perfeet radius.
The Jtiiinrrai^ (PI. vin, figs, 4" and 4/^ is consideralily expanded dorso-
vi'utrally at the proximal end through the dev<dopinent of a very heavy pectoral
ridge extending to the nuddleof the shaft. The distal en<l is greatly broadeiu'd,
its width equaling two ihii'ds tlu- length of the bone. In either inferior or
superior view the middle of the shaft appears more slender than is actually the
case, owing to the fact that the expanded ends are twisted at right angles to each
other. Poth the pi'oximal and distal ends seem to be deeply excavated, and
evidently supported large cartilaginous caps. In one specimen (PL viii. tig. Ah)
1"
from above, X %. f, eoracoid ;
N. scaimla; //. Inimerus; R,
radivis; V, uhia.
22 CALIFORNIA ACADEMY OF SCIENCES
a small foramen is seen near the distal end of the pectoral ridge. Although
it is quite small it probably represents an epicondvlar foramen.
Tlic humerus of T. shasfenfiis (PI. viii, fig. <S) is perhaps a little more slender
than ill T. alexartdrae, Init is imperfectly rejiresented in the figures, as it is
considerably weathered.
The radius (VI. viii, fig. o) is shafted, but shows considerable <listal and
proximal expansion. Its length is about one half that of the humerus. The
■uhta (I'l. wii, figs. () and 7) is convex posteriorly and concave anteriorly, show-
ing no median constriction.
Several rounded ossicles resembling the phalanges of Bapfaaodon have been
found associated with the limb and arch bones of the type specimen. Undoubtedly
they represent carpals or })lialaiiges, and there is a possibilitv that some at least
are phalangeal elements.
The fyi^e nf limb represented in this form is that of an aquatic animal, as is
shown particularly in the extreme shortening and broadening of the humerus
and of the ('}>ipodial liones. Such indications as are given in the possible char-
acter of the phalanges would also point in this direction. The specialization of
the lindi is greater than that in the I'roganosauria, ( -horistodera or Parasuchia.
It can perhaps be best compared with that of the Plesiosaurs or with the Triassic
Ichthyosaurs. The humerus is, however, a little more slender medially than in
the Ichthyosaurs. If tin- rounded ossicles are really phalanges, it is evident
that the limb was no longer serviceable to any extent for land or shore locomo-
tion but had become the specialized paddle of a purely aquatic type.
HABITAT, LOCOMOTION, FO(JI).
The remains of Thalattosaurs are known only in purely marine deposits
containing little or no material of terrestial origin. They are associated with a
fauna consisting of numerous forms, both vertebrate and invertebrate, which
are not known to have existed away from marine areas. In the structure of the
skeleton we find the abbreviated and broadened proximal segments of the limbs,
the slender snout with prehensile terminal teeth, and the median superior nares,
indicating a j^urely aquatic type. There can scarcely be room for doui)t that
the Thalattosaurs as a group were typical marine forms.
The larger and more specialized species comprised in the genus Thalaito-
saurus were strictly ]iatatory. They may have visited the shore but, like the
Plesiosaurs, were better fitted for swimming than for crawling. Of the smaller
Nectosmirus we unfortunately do not know the limbs. They ma}' have been con-
siderably less specialized than in the other genus, and the animal to a corre-
MERRIAM THK THALATTOSAT'TilA Zo
spondingly greater degree a shore dweller. NectosaurnH is, however, found in the
same deposits with the otlier forms and appears to he as common as the others;
so that it is safe to eonsi<lcr it as liaviiig passed tlie greater part of its life away
from the sliore.
From what we know of the vertebral eoluiiin of TlutlattDsawrm it appears
that the animal had a relatively short neck and a long dorsal region, the propor-
tions heing near tiiosc in the vertebral eolunin of some Mosasaurs. Only the
anterior portion of the caudal region is known. The slender, rounded neural
spines with well develo})e(l zygapopliyses seen hert^ are not such as commonly
appear in forms Avitli a highly specialized sculling tail, and it is hardly probal)le
that a caudal tin of hirge size was developed.
The anterior limbs evidently formed paddles of moderate size. The pos-
terior pair n)ay have been larger, in compensation for lack of a strong
sculling tail. It is, however, possible that as in Geosaurus the hind limbs were
not typically uatatory and that the distal end of the tail was vertically expanded.
No specimens have yet been found which are well enough preserved to show
any remains of the stomach contents, and we have no delinite evidence concern-
ing the food of the Thalattosaurs, more than is furnished by the general structure
of the animal. The character of the paddles, the form of the skull, and the
presence of slender prehensile teeth in the terminal ])ortions of the jaws would
indicate that they fed in part upon some swiftly moving prey which was caught
by a quick snap of the jaws, deglutition being assisted by the c'urved teeth of the
pterygoid. The heavy vomerine and posterior mandibular teeth may have been
used for crushing the light shells of ammonites, which existed in vast numbers in
the same seas.
AFFINITIES AND SYSTEMATIC POSITION.
As would l)e expected in forms occurring in the Triassic, the Thalattosauria
exhibit many features which aic generally considered as j)rimitive. Among
these are the biconcave vertebrae, single-headed ribs, w(dl developed abdominal
rib plastron, narraw sca[)ula, plate-like coracoid, sculptured jaw elements, strong
vomerine and pterygoid dentitions, and the presence of a parietal foramen. It
is, however, bj^ no means a primitive type, but is really one of the more specialized
of the reptilian groups of the Triassic. Peculiar or specialized characters
appear in the structure of the limbs, in the rostral region of the skull, in the
position of the narial openings, in the relations of the nasals and premaxillaries,
in the character of the parietals, and in the nature of the dentition.
Owing to the considerable degree of specialization of the particular kind
which we find in this group, it would almost necessarily be true that any order
24 CALIFoItMA ACAOKMY (IF SCIE.NCKS
in which it could he phiccd would be comprised mainly of acjvuitic forms. Its
relationship to any other than an a(|uatic jjroup will probably be a weaker bond
tlian ordinal affinity, and very close sinnlarity must be souiiht in sdine of the
natatory types.
The characters of the Thalattosaurs are such as to brinji' them into more or
less definite relationship to a consideral)le number of ijroups. In some cases
this is due to similar adaptation. To several (juite different groujis they show
true affinities of nearly the same degree, indicating relationship through a com-
mon ancestral type or group from which they have all originated. The most
important resemblances and affinities are discussed somewhat in detail before
presenting th-e conclusions reached through these comparisons.-
Iclitlnjiixdiiriini Affiiiitie.^i. — The Thalattosaurs inhabited the same seas with a
large group of Ichthyosaurians and showed much the same Icind of adaptation
carried also to a high degree. The Ichthyosaurs are generally helil to be nearly
relate<l to the Rhynchocephalia, and the Thalattosaurs are evidently near rela-
tives of that group. Under these circumstances we should expect to lind the
Ichthvosaurs and Thalattosaurs showing similar structure and giving evi<lence
of near relationsliip.
In the extremities, where adajitation to ac^uatic conditions is most readily
and distinctly expressed, we find both forms exhibiting the typical natatory
type. In the Ichthyosaurs the [iropodial and epipodial elements show a some-
what greater degree of abbreviation. Unfortunately we do not as yet know the
character of the termimil portions of the paddles in the Thalattosaurs and can
nmke no comparison here. As far as is known, the iclithyosaurian paddles seem
to have attained a slightly higher degree of specialization.
In the vertebrae of the tAvo groups there are considerable differences in the
character of the neural spines, in the zygapophyses and in the attachment of the
up})er arches to the centra. The difference in form is particularly noticeable in
the anterior caudal region. The pectoral girdles are somewhat similar, but as
far as is known the pelvic arches are c^uite different.
In the skull we find the nares occupying much the same position in both
groups, and the premaxillaries are elongated in both. In the Ichthyosaurs the
premaxillary elongation is extreme and the nnixillaries are not only relativcdy
small but seem actually to have suffered recluction. Distinctive skull characters
separating the Ichthyosaurs widely frcnu the Thalattosaurs are noted in the
absence of an inferior temporal opening and of a coronoid elevation, the separa-
tion of the postfrontal and postorbital, the enormous size of the nasals and their
different relations to the premaxillaries, the different relations of the parietals
to the small frontals and to the superior temporal openings, a different structure
Mi;i;i;iA.\i — tiik TiiAi-ATT<isAri;i a 25
in the palathu' ivuioii. tlii' lack of voiiu'riiif and ptcrvuoid teeth, ami the isodmit
or only slightly differentiated ehararter of the <i'nathie dentition in all the known
species of this epocli.
Some of the structural differences separatini:' these two groups are doid>tless
to he correlated with difference in liahits; in other words, they may he
ascribed to somewhat different kinds of adaptation. The Ichthyosaurs were
largely fish eaters. They therefore had no great nee(l of a liea\-y vomerine den-
tition. In the same way the presence of a strong coronoid projection on the
thalattosaurian jaw may be correlated with somewhat increased muscular power
used in crushing with the broad teeth of the prevonier and of the posterior por-
ti(m of the dentarv. ()ther differences may be due to great increase in the size
of the orbits in the Ichthyosaurs, although this may be considered as due to
better opportunity for increase in size in that group owing to fundamental
difference in the original structure of the skull.
These facts are particularly significant when we ccmsider their bearing on
questions concerning the origin and relationships of the Ichthyosaurs. If the
Thalattosaurs and Ichthyosaurs were both derived from the primitive Diaptosauria
and were both typical marine forms following somewhat similar lines of adapta-
tion, Avlw ai"e they so different? With similar environmental conditions we
would expect l)ut little divergence. It is evident that in this case we have one
of the following possibilities: 1. The Thalattosaurs and Ichthyosaurs have come
from the same stock but have followed quite different lines of adaptation;
2. They have come from the same stock and have followetl only slightly different
lines of adaptation, but have, one or l)oth. been in existence for a very long
period; 3. They have originated in different groups.
Concerning the first possibility — there is reason to believe that the groups
differed somewhat though not greatly in food hal)its, but that in a broad way
the kind of adaptation was the same. It was such as wtuild generally tend to
jiroduce a certain degree of convergence. Th<' kinds of adaptation we should
presume to differ less than among the Cetacea, while the structural differences
are as great or greater than we find produced in not h^ss than four periods of
evolution in that more rapidly living aquatic grouj).
Regarding the second case — we unfortunately know as yet but little con-
cerning the early history of either group. Thalattosaurs are known as early as
the beginning of the Upper Triassic, and the oldest h'hthyosaurs which we know
are found in the lower part of the Middle Triassic. The Ichthyosaurs certainly
appear to be somewhat more specialized than the Thalattosaurs and are pre-
sumably someAvhat older, so that we could imagine a slight difference in adapta-
tion acting through a long period as having resulted in llie prtxluction of these
26 CALIFORNIA ACADEMY OF SCIENCES
veiy different types out of tlie same stock. The Iclitlu'osaurs may have taken
to the sea earher, and the Tlialattosaurs have originated from a later and there-
fore somewhat different pliase of the same group. On tlie otlier liand the
development of such differences as we see here must have required much time,
and it may well he questioned whether the time of origin of the lehthyosaux's
may not date back so far that it would be straining a point to call its ancestors
Diaptosaurian or even Diapsidan.
The remaining situation, in wliicli we would have the two groups converging
from fundamentally different stocks, seems in many respects the most natural
relation. At any rate, the two groups must be considered as widely separated,
and neither may be judged to be ancestral to the other. If they are not closely
related ami it should appear that of the two the Tlialattosaurs are nearer to the
Rhynchocephalia, we ma}- perhaps reasonably (juestion the rhynchocephalian or
diaptosaurian origin of the Ichthyosaurs.
ParasKcJilcni Characters. — The general skull structure of the Tlialattosaurs has
a certain degree of resemblance to tliat in Belodon, particularly in the rostral and
temporal regions. The position of the nares is similar, as also tlie general form of
the premaxillaries and maxillaries, though the premaxillaries do not separate the
nasals and reach the frontals. The superior temporal openings are similarly
situated low down between the upper temporal bars, and the parietals bound
the anterior side to a greater extent than is usual. There is also some similarity
in the structure of the palate, and the gnathic dentition of Behxlon is not unlike
that of Thakittnsanrus pc^rini. Taken as a whole, however, the two skull types
are very dissimilar. The superior nares of Belodon are in the large nasals; the
premaxillaries do not reach hack to the frontals; large antorl)ital vacuities are
present; the lachrymals are large, while the prefrontals, frontals and parietals
are relatively very small; the postorbital and postfrontal are separate; tliere is
no pineal foramen; the form of the quadrate is very different from that of Tlta-
lattosavnis; the palatine borders the inferior nares externally; the coronoid is
small and inferiorly situated; there are no teeth on the prevomers or pterygoids;
and there is a large mandibular vacuity. These differences together with the total
dissimilarity in the structure of the vertebrae, ribs and lindjs show that the two
groups are ordinally distinct. The general outlines of the structure in both arc
those of the primitive diapsidan Reptilia. Both are aquatic types and to a slight
extent this has tended to bring them nearer together. The possibilities of
evolution in the marine Thalattosauria were, however, much greater and also
specifically different from those open to the fresh ivater Parasuchians, and the
result of specialization has been the production of very different forms. As
different as these two ai'e. it may he noted that they are at least as near together
as the Tlialattosaurs and the Ichthyosaurs, although the latter are marine.
MERRIAM — THE THAIrATTOSAT'inA 'It
Relationship to Squamata. — Althougli tliu Tluilattt)saurs evidently possessed
two temporal openings, with a complete lower temporal bar, their resemblance
to the lacertilian and mosasaurian branches of the S([uaiiuita arc so prominent
as to demand consideration of possible relationship to them. The general aspect
of the mandilile is that of a rej)resentative of the S(jnamata, though it is also
approached in the Rhynchocephalia. The form, situation, and prominence uf
the coronoid are such that the posterior portion of tli» jaw taken alone could
scarcely l)e considered as other than lepidosaurian.
( )n the superior side of the skull there is a noticeable similarity to the
Mosasauria. In both the Thalattosaurs and Mosasaurs the rostral region is
narrow ; it is generally somewhat elongated and acute terminally. The nares
are set w(dl back and the premaxillary is produced posteriorly as a stem or bar
which meets tlie frontals. There are no discrete nasals in the Mosasaurs and they
are generally supposed to be united with the posterior end of the premaxillary
bar as in ]"aranus. Should it appear that they have been lost and the fronto-
premaxillary connection be immediate, the structure in this region would be
very similar in the two groups.
In the posterior part of the Mosasaur skull the l)road frontals are often
partly arched around the anterior ends of tlie parietals as in the Thalattosaurs,
while the postfrontal and postorbital have partly united. So far as can be
determined, there is room to suppose tbat tlie upper portion of the temporal
region may not differ greatly in the two groups. The quadrate of the Thalatto-
saurs is in general of rhynchocephalian type and the widely extended anterior
wing is not seen in the Sc^uamata, but the presence of a strong external wing
and the incipient development of a posterior hook make it begin to show resem-
blance to the type seen in the Mosasaurs and Lizards.
In the characters of the limbs and arches there is much that is similar.
The vertebrae and ribs differ, Init perhaps not so fundamentally as would a])])ear
from superficial examination.
On the whole the resemblance to the aquatic Squamata is v<'rv striking;
but it can not ove~rbalance such characters as the evident presence of a lower
temporal arch, the existence of a strongly developed vomerine dentition, an
immovably lixed mainly rhynchocephalian (quadrate, abdominal ribs and very
})rimitive vertelirae.
While it is not possible to place the Thalattosaurs in the S(|uamata. as that
grou}) is at present defined, it is not improl)able that the primitive Lacertilians
were closely related to or derived from the land or shore forms from which the
Thalattosavirs were deriveil. Adaptation to a(|uatic life would tend to make the
Thalattosaurs take on rapidly a certain set of characters which would appear
28 OALIFOKNIA ACADEMY OF SCIKXCKS
again in the Mosasaurs. This specialization would at the same time take tlic
Thalattosaurs out of the direct line of I'volution. It is to be noticed in this
connection that the smallest and least specialized form, seen in Nectosaurus, is
nearer the Lacertilia than the large]- and more specialized Thalattosaurus.
In PaligiuDia Broom, of the South African Triassic, we have represented an
undoubted Lacertilian with the lower temporal arch absent and only a minute
process projecting from the posterior side of the jugal. Tlie ([uadrate is typically
lacertilian as are also the relations of the elements in the upper temporal bar.
This form shows that the characteristics of the Squamata were expressed very
early and makes more probalile the discovery of lacertilian tendencies in early
diaptosaurian groups.
Relationshi-p to the Proganosauria. — As possible close relatives of the Thalat-
tosaurs, the Proganosauria claim especial notice,- being a group of ratlicr prim-
itive aquatic forms having affinities with the Rhynchocephalia and occurring
earlier in geological time than the Thalattosaurs, and therefore possibly ancestral
to them. Ihifcn-tunately the part of the thalattosaurian skeleton of which we
have the best knowledge, viz. the skull, is the most imperfectly known part in tlie
Proganosauria. Osborn considers the skull probably double-barred, though the
structure of the temporal region is as yet unknown. The position of the superior
nares and the .structure of the palate are likewise unknown. Teeth are present
on the roof of the mouth on what are supposed to be the palatines, while in the
Thalattosaurs they are absent from the palatines, and present on the prevomer
and pterygoids. The skull is considerably longer and more slender in tlie Pro-
ganosauria and the long, slender teeth are more numerous.
In the structure of the better known parts of the sktdeton of the Progan-
osaurs the separation is wide. The small centra and greatly expanded upper
arches of the vertebrae and tlie peculiar narrow-headed ribs of the Proganosaurs
stand in strong contrast to the relatively small upper arches and the broad-
headed ribs of the Thalattosaurs. In the pectoral girdles of the two there is
some similarity excepting in the scapula. The plate-like pelvis of the Progan-
osaurs is much more primitive than that of the Thalattosaurs and the limlis of
the former have not gone nearly so far in specialization, particularly in the
shortening and broadening of the epipodial elements.
Relationship to the Choristodera. — The aquatic diaptosaurian forms included
in the Choristodera resemble the Thalattosaurs mainly in that they are acjuatic
and have rhynchocephalian affinities. Here, as in the Thalattosaurg, there is a
vomerine dentition l)ut the teeth are small, very numer(nis, of an entirely differ-
ent form, and are set in several rows. The pterygoitl dentition is also different
and the palatines bear teeth. The Choristodera are farther distinguished from
Mi;i!i;iA>[ THK THALATTDSATItIA 29
the Thalattosaurs bv the more skMuk'r snout, the terminal jiosition of tlie nares
and tlie corresjjondintilv different structure of tlie rostral re,s;ion, the absence of
a j)ineal foi-anicn and of a coronoid process, the robustness of the ribs and the
bicipital ai'tieidation of those in the anterior dorsal region, tbe different form of
the elements in botb pectoral and peh'ic arches, and the rclativ<'ly but little
specialized limbs.
In the lenjfthening of the snout tbe ( 'iioristodera are more specialized than
the Thalattosaurs. l)Ut the ternnnal position of the external nares shows the kind
of specialization which we hnd mainly in aquatic reptiles belonging in fresh
water, while the position of the nares in the Thalattosaurs is the form of special-
ization seen generally in marine types.
Wlien we consider along with other things that tlic ( "Iioristodera are in some
respects much less specialized than the Thalattosaurs, and that they occur two
geological periods later, it is evident that they are not closely related.
Reseviblaiice to Proterusuchus. — Some interesting resemblances to the Thalatto-
saurs are shown in Pmternsxchvs recently described l)y Broom. ^ This important
form is known oidv from the anterior portion of a skull reciMitly discovereil in
the Karoo beds of Tarkastad, South Africa. In it we find dentigerous prevomers
and pterygoids with edentulous palatines. The prevomers reach back to meet
the pterygoids broadly. On the upper side of the pterygoids are high, thin
vertical plates. The characters of this form am[)ly justify its determination by
Broom as "a primitive Rhynchocephalian which shows a considerable degree of
specialization along a line which gave rise to the crocodiles. . .'"
The cond)ination of characters found in Prdfcrdsuclnis is in som(> respects
similar to that seen in Th((laftosaurus, and as is shown i)y i>room for Proterosiirlnix,
the palatine region exhibits a general resend)lance to that of Pnivolojilioti. In
other characters, as in the presence of large antorbital vacuities, the anterior
position of the external nares, the position of the internal nares farther forward
and separated by the main bodies of the prevomers, in the absence of a coronoid
process, and in the large size and hcavv fangs of the slightly differentiated teeth,
Proferosuclius shows itself to be quite different from Thalattosaurus. The resem-
blance exhibited by these forms is evidently in the main due to their approxima-
tion to the type of the primitive Rynchocephalia. Such similarities as we tind
are not sufficient to permit our including them both in the same order. In
adaptation to acjuatic con<litions Proterosiiflnis might have led to some such foi'ms
as the Parasuehians. while the Thalattosaurs stand as a type very different from
this order.
ReJationxhi p to the Protoro^anr'nt. — N'ery close aflftnity with any of the forms
1 R. Broom, .\nn. South .\frican Mus. v. 4, art. 7, p. 159, pi. xix. Nov. 1903.
30 CALIFOKNIA ACADEMY OF SCIENCES
ill tliis order is precluded by the totally different structure and function of the
limbs, the character of the i)elvis, and to a considerable extent also of the lower
jaw and the facial region.
The skull of Palaeohatteria differs from tliat of the Thalattosaurs in tlie
terminal position of the superior nares, the small and short premaxillaries,
large maxillaries and lachrymals, very large nasals, separate postfrontal and
postorbital, absence of coronoid or at least of a prominent coronoid projection,
and in the })resence of large prehensile teeth on the posterior [)ortion of the jaws.
It might be presumed that the greater number of these differences could be
brought about by retrogression of the narial openings with corresponding
enlargement of the premaxillaries, in the evolution of an aquatic form from a
type originally like Palaeohatteria. There are, however, few real similarities con-
necting-P«/aeo/t«^<er/o and the Thalattosaurs which would not at the same time
show affinities Avith the majority of the older diaj)sidan orders. While such
modification may be considered possible, there is nothing to show that it has
actually occurred.
The relationship to Protorosaurns is hardly nearer than to I'dhicdhatfcr/a.
The limbs, girdles and vertebrae are very different, and the skull is not more
similar. The facial region in some respects seems to present a stronger resemblance
than to PiiaeoJtattcria and if, as Seeley has suggested, the openings immediately
in front of the orbits in Protorosaurus are really the superior nares, there would
be an important feature common to the two. The nasals are, however, very
large, reaching far forward as in the Ichthyosaurs, and the premaxillaries appear
to have no posterior stem. In the palatine region we find the prevomer long
and slender, and the palatines swinging around the narial openings and coming
into broad contact with the prevomers in front of the nares as well as behind
them.
Evidently no close affinities are to be found with the Protorosauria, and
while we must suppose the Thalattosaurs to be derived from Permian land or
shore forms, it would not be possible to unite them with this group or even to
consider the Protorosauria as the ancestral type. As has been shown by Seeley,
Nopcsa, (_)sborn and others the trend of evolution in the Protorosauria was
already decidedly toward the development of specialized land forms, as seen in
the Dinosauria.
The Thalattosaurs are probably derived from land forms, as is evidenced
b}' the character of the pelvis and of the neural spines of the vertebrae. The
Protorosaurs probably come nearer than any other group to this primitive type,
but are not themselves the ancestral forms which we seek.
MERRIAM THE THALATTOISAX^RIA 31
Rclatioiiiiliip to titc Iilnjiiclioccphaliu. — lu a large number of the skeletal
characters, strong similarities to the Thalattosaurs are found in various mem-
bers of the Khynchocephalia. In the general plan of the skull there are many
points of resemblance, and the uniformity of this resemblance throughout the
various parts is particularly noticeable. In some respects we find in
the Rhynehocephalia approximations to thalattosaurian characters not seen
elsewhere.
In the superior temporal region the similarity of Sauranodon and Pleuro-
saurits to the Thalattosaurs is evident. The parietals here extend around the
anterior ends of the upper fenestrae as in Belodon, and in both of these genera
thej' meet the squamosals on the outer side of the upper temporal openings.
In the structure of the arches and ribs many common characters are found,
although the vertebrae are not closely similar. The similarity of the more
slender pelvic elements is particularlv noticeable, being closer than betAveen the
thalattosaurian elements and the primitive plate-like pelvis of the Protorosauria
and Proganosauria or the liroad pelvic elements of the Choristodera.
As discriminating characters, we find that no true Rhynchocephalian pos-
sesses a vomerine or pterygoid dentition or shows the degree of adaptation of the
limbs and skull to aquatic conditions that we find in the Thalattosaurs. No
member of this order has such highly specialized limbs and in none do we find
the thalattosaurian structure of the rostral region. Pleurosaurus and Acrosaurus
were aquatic forms, but the limbs were only slightly modified. The structure of
the nasal region in Pleurosanrus approaches that of the Thalattosaurs but does
not appear to be the same. Moreover, in Pleurosaurns where we find some of the
closest i'e.semblances, the structure of the lateral temporal region appears very
different. From Lortet's figures^ it would seem that there is no lateral temporal
vacuity here. Such was also the impression obtained by the writer in a hasty
examination of his specimen.
As all of the Rhynehocephalia which we have for comparison are much
younger than the Thalattosaurs, an<l are all in many respects less specialized, it
is useless to atten;pt to place them in any ver^- close relationship to the Thalatto-
sauria. It is probable that they are derived from a persistent land or shore type
from which the Thalattosaurs are an early offshoot.
Conclusions.
I'^roni the comparisons that have been made, it is evident that the Thalatto-
saurs are to be considered as an independent group. The orders with which
1 Kept. Foss. du Bivs'sin du Rhone, 18!M. PI. viii, tigs. 1 and 2.
32 OALIFOnXTA A<AnE.MV ol' SCIENCES
they liavo most in coinnion are either those eoiiiprisiiig typical atjuatic forms or
th(jse in wiiieh rliyncliocepluilian characters are very prominent. Even where
we liavc the characters of an a([uatic animal (U'veloped in a form of the rhyncho-
eephalian type, we fail in every instance to find closer afhnitv than the l)on(l
between the iMosasauria and the Lacci'tilia or tliat between the ( 'horistodera and
the Rhynchoceplialia.
Dnrin^i;' the [leriod in which the Thahittosaurs tloiu-islied there were three
other impoi'tant i^ronps of marine rej)tiles in existence. These were tlu' Notho-
saurs, Ichthyosaurs and l'laco(h)nts, none of which were closely related to tiie
Thalattosauria. Of tiie older reptilian orders, the Protorosauria and Progano-
sauria are nearest the Thalattosaurs. The first of these comprises terrestrial types
with (jnite a different structure and showing already in the Permian that the
tendency of their evolution was toward highly specialized land forms. The
Proganosaurs, also of the Permian, exhibited a different type of evcdution in the
skull, ril)s and vertebrae, and had much less specialized limbs.
Of the younger orders the ("horistodera and Iv]iyncliocej)halia show notice-
al)le similarity to the Thalattosaurs in their fundamental skeletal plan. The
affinity with the ("horistodera is on the whole weak, as the skull, arches and
lind)s are decidedly different. They represent a distinct aquatic type which
must reach back to the primitive Diaptosauria for a true expression of its affinity
with the Thalattosaurs. The Khynchocephalia s. str. as shown in the luimerous
types ordinai-ily classed in it show more real kinship with the Thalattosaurs than
most of the other orders. Affinities are expressed in varying degrees in Sphcvn-
ihni. Uoniensaurnx, PIcnrnsanriis and Sduranndon. It is, however, to be doubted
whether all of these forms s!iovd<l be grouped in one order. In the possession of
luunerous jieculiar characters, both primitive and specialized, and ])artii-ularly
through the group of characters which has arisen owing to the higher degree of
adaptation to acjuatic conditions, the Thalattosaurs show themselves distinctly
separate(l from the true Khynchocephalia.
The resend)lances to the S(|uamata are striking. They are evidently fouiide(l
in a large measure on parallelism, but may also be due to (dose affinity between
the primitive Thalattosaurs and the ])ai'ticular group in the primitive Piaptosaurs
from which the S(puimata originateil.
The Thalattosaurs rejiresent an earlv adaptation to marine c(mditions of
that division of the Reptilia which has persisted in measurably priniitiN'e form
in the Khynchocephalia. l)uring the early iiistoi'y of that grouj) it ga\(' rise to
a numerous company of forms taking (piite divergent paths in their evolution.
( )f the older onlers (uily the Progauosauria were a(iuatic. They appear, how-
ever, to have been limite<l to fresh watei'. The Thalattosaurs are eviflentlv the
MERRIAM THK THALATTOSAURIA 33
marine representatives of this ^reat rhynchocephalian or diaptosaurian group. In
accommodation to marine conditions their specialization toward tlic natatory-
type was carried farther than it would naturally go in forms living in the more
narrowly circumscribed bodies of fresli water. In sea forms a continued or sus-
tained existence in the water, and even some distance away from the sliore, was
probably advantageous. !^uch a tendency would necessarily result in the evo-
lution of the only type of extremity that would be serviceable; namely, the
|)a(ldl('. In lK)dies of fresh water where the shore is in general easilj- accessible
the functions of the limbs would be divided between crawling and swimming.
Of the seven orders tentatively placed in the Diaptosauria by Osborn none
are composed of typical natatory, marine forms. It would liave been remarkable
liad tlicre not been developed in tlie adaptive expansion of tliis group just such
a type as is represented here. In tlie relation of the Thalattosaurs to tlie other
diaptosaurian orders we find a situation similar to that in the i^quamata, the
Tiialattosaurs showing the same kind of adaptive specialization away from the
primitive Diaptosauria that the Mosasaurs have exhibited with relation to the
primitive Lacertilia.
GENERIC AND SPECIFIC CHARACTERIZATIONS.
In general, the structure of tlic known specimens indicates close relation-
ship of the forms wliich they represent. There is, however, a certain degree of
variation, particularly of the dentition and limbs, which is best expressed bv
separating them into two or mcjre genera.
THALATTOSAURUS Mcrriam.
Bull. Dfpt. (u-ol. Iniv. Calif, v. 3, no. 21, p. 419.
Type f^pecios. TlidldftdMno-iis aJrxnnd me.
Posterioi' numdibular teotli, broad-elliptical in cross-section, low-crowned:
median teeth increasing in lieiglit anteriorly through the develo})inent of
an antero-external tubercle. Anterior mandibular and premaxillarv teeth
slender conicah MaxiUary teeth conical in one species, imperfectlv known in
the others. Humerus sliort, expan(h'(l distally, witli high pectoral ridge. Radius
and ulna much shortened.
(S)
34 CALIFORNIA ACADEMY OF SCIENCES
Thalattosaurus alexandrae 3Ierr>am.
Plates I, II; Plate IV, Vu:. 1 ; Plate V, Figs, lfi-2/,; Plate VI; Plate VII, Figs. 1-.3, 8-9;
Plate VIII, Figs. 1-2, -ta-6.
Bull. Drpt. Ccdl. Univ. Calif, v. 3, no. 21, p. 419.
Type spediiK'n No. 9085 Univ. Calif. Palae. Coll.
Tliis is tlie largest species of tlu' group. The known siieeinicns appear to
represent individuals attaining a length not far from two metres. Neural spines
of vertebrae not greatlv widened. Propodial and epipodial limb elements and
scapula considerably expanded. Nasal openings long, portion of nasal elements
behind the nares relatively short. Slender anterior teeth with widely' spaced striae.
Posterior mandibular teeth ver\' low-crowned, l)utton-like. The number of teeth
on the dentary appears to have been eighteen.
A large part of our knowledge of the Thalattosauria has been obtained
through the study of this species, of which several representative specimens are
known. All of the material representing this form has been obtained in the
Trachyceras horizon of the Hosselkus Limestone. No occurrences are known
outside the Shasta region of California.
MEASUREMENT.S.
Vertebrae.
mm.
Anterior dorsal (No. 9084), height of centrum 20
width " " 23
length" " 16
" " " height of upper arch 46
" " " antero-posterior diameter of upper arch at middle
height of spine 13
" " " transverse diameter of uj)per arch at middle height of
spine V(5
Anterior caudal (No. 9085), height of centrum 30
" " " width " " 13
length" " 18
" " " height of upper arch 48
" " " antero-posterior diameter of upper arch at middle
height of spine 8 ,
" " " transverse diameter of upper arch at middle height
of spine 6
la, approximate.
MERRIAM THE THALATTOSAURIA 35
Arches.
Coracoid (No. 9085), antero-posterior diameter 65
transverse diameter of median portion 33
Scapula " greatest length 55
Ischimn (?) " " " 72
'• " width 26.5
Pubis(?) (No.9044), " lengtli 106
" width 47
Linihs.
Humerus (No. 9084), greatest length 75
" '• " width, proximal end 39
" " " " median portion 21
" " " " distal end 52
thickness of distal end '. 18.5
Radius " " length V,40
" " " width, distal end a29
" " " " median portion 15.5
Ulna (No. 9085), greatest length 40
" " width, median portion 25
Thalattosaurus shastensis, n. sp.
Plate III; Plate IV, Figs, lio-e; Plate VII, Fios. 4, 7; Plate VIII, Figs. 3, 7, 8.
Type specimen No. 9120 Univ. Calif. Palae. Coll.
Conipai'ed with T. akxandrae tlie individuals are consideral)ly smaller: the
scapula, liunierus and ulna more slender; the nasal openings shorter and that
portion of nasal bones behind the openings longer and broader; the neural s})ines
of the dorsal vertebrae are possibly shorter. The conical teeth associated with
the type specimen show more numerous and more closely set longitudinal striae
than are seen in tlie jaw teeth of T. alexandrae. There is of course a possil)ility
that these teeth belong to the pterygoids and not to the jaws.
This species appears to be very near the type form of the genus and may be
shown later to be identical with it, possibly representing young individuals.
There are, however, several specimens in the collection which seem to have the
same characters and to be slightly removed from T. alexandrae.
This form is not uncommon, and ranges from the Trachyceras horizon almost
if not quite to the top of the Hosselkus Limestone. It is known only from the
Triassic of Sha.sta County.
la, approximate.
36 - oaltfornia academy of srie>m'ks
Measurements.
mm.
HuniiTUs (No. 9120), length 32
Ulna " " 21
greatest width 11
Thalattosaurus perrini, n. s]).
Plate IV, Fiu. 3; Plate V, Fig. 3; Plate VII, Fi(i. 6.
Posterior mandibular teeth with hiterally compressed and obtuse but not
greatly depresssed crowns, grading anteriorly into a slender conical form on the
anterior portion of the jaw. Maxillary teeth slender conical, set in deep pits.
The dentition of the dentary and the maxillary are well shown. The den-
tarv holds an interrupted series of twelve teeth with spaces for several more
among them. The entire number lias probably been sixteen to eighteen. The
posterior ones have low, broad, laterally compressed crowns. Tlic individuals in
the middle of the series were short, broad, and leaf-like, their margins being verj'
close together. The anterior members of the series have a shorter antero-posterior
dianreter, higher crowns, and a slender conical form without lateral compression.
The most anterior tooth, seen only in oblique section, shows strong longi-
tudinal striations or ridges on its surface. The most posterior teeth are close
together and in shallow pits. The anterior ones are deeply set and are more
widely spaced.
On the maxillary there are five teeth of slender conical form, witli spaces for
one or two more. They are in deep, distinct pits.
As much of the vomerine dentition as is known is very similar to that of
Tha laftosauru s a lexandrae.
The general characters of this form are tliose of a typical Thalattosaurian.
The type specimen, the only known sjiecimcn of this species, was the first
Thalattosaurian discovered. It was found by Professor James Perrin Smith in
the Trachyceras beds of tlie Hosselkus Limestone at Smith Cove, near Scjuaw
Creek, Shasta County. There was exposed on the slab only a prevomer with its
peculiar, bhmt teeth. Later the portion of tlie skull sliown on Plate iv, figure 3
was exposed by preparation witli steel points and l)v etching with very dilute
hydrochloric acid. After the jaws had been partly uncovered, the writer pub-
lished a note on the Triassic Reptilia from Northern California,^ in which this
specimen was referred to as a Shasfasaurus with a heterodont dentition. Later
it was discovered that it could not belong to the Ichthyosauria, but the true
affinities were not known until after the discovery and study of the type of
Thalattosaurus alexandrae.
I Science, n. ser. t. 15, p. 411.
MERRIAJr THE TH ALATToSA ri! I A 37
This species is (|uite distantly removed from T. alcxandruc in dental char-
acters, and may he found to represent a distinct genus.' Although the posterior
mandilnilar teeth differ mucli from those of T. alezandrae the difference is only
one of degree. So far as known the character of the maxillary teeth seems to he
quite different hoth as regards form and insertion. Satisfactory comparison can
not he made, however, until we know more of the dentition of T. alerandrae.
NECTOSAURUS, n. ovn,
Nectosaurus halius, n. p;en. ami sji.
Platk I\", Fic. 4((-.'); Plate V, Figs. 4, (i; Pi.atk \'II, Fig. -5.
Type specinu'ii No. 9124 Tniv. Calif. Palac Coll.
Fronto-parietal region simihir to that of 'f/i(il<ittii.-<(nin(s. Quadrate with
exterior wing. Mandible of Incertilian type. Crowns of jiosterior mandibular
teeth conical, acute, slightly recurved, coarsely striated.
To this species are referred a portion of a skull constituting the type, and a
number of isolated bones which seem to belong here. The type was the first
thalattosaurian specimen to be carefully studied. Manuscript was originally
prepared for its description as a primitive Lacertilian but was withheld from
publication until more material should be obtained.
While the mandible anil quadrate are of a lacertilian type, thalatto-
saurian affinities are indicated by the character of the fronto-parietal region.
The frontals (Fl. iv, fig. -ia) have the same form as in Thalaftosaurus. They
receive the premaxillaries between them anteriorly, and clasp the parietals
posteriorly. There is also present a portion of a prefrontal and a post-fronto-
orbital. A cross-section of a vertebra (PL vii, fig. 5) shows the upper arch
apparently firmly connected with the centrum.
This genus contains the most primitive forms of tlie Thalattosauria and will
probal)]y furnish additional evidence concerning tlieir relationships when its
skeletal structure is better known.
N. hal/Ks appears to he present at nearly all horizons of the Hosselkus
Limestone.
In Plate v, figure (), tliere is shown a small jaw repi'esenting a type c^uite
common in the Hosselkus Limestone. While not seen in association with
certainly recognizable NccfosaHrns remains, it is doubtfully referred to that
genus. The dentigerous palatal element sho\vn in Plate v, figure 4 is still more
doubtfullv determined as belonging here.
1 Should this type be found to be generically distinct from ThalattosauruH the generic name Scenodon will be used to
distinguish it.
38
CALIFORNIA ACADEMY OF SCIENCES
EXPLANATION OF PLATE I.
Thdldttosuvnis alexandrae.
Type specimen. All fiijures three fourth.^ natural size.
Cranium slightly distorted, the anterior
Fig. 1. Anterior portion of eraniuni and niandilde
end of the maxillary being covered.
Fig. 2. Palatal view of cranium.
Fig. 3. Inner side of mandible.
Legend.
F, frontal
Pf, prefrontal
N, nasal
A, doul)tful element anterior to
narial opening
Pm, premaxillary
M, maxillary
L, lachrymal
PI, palatine
J, jwgal
V, prevomer
/, inferior narial opening
Sa, supra-angular
An, angular
D, dentary
Sp, splenial
a, h, c, sections of cranium.
PL II, figs, la, \h, Ic.
See
JV and A in fig. 1 are situated in the superior narial opening.
Memdirs CalAcad.SciVdlY
[Merriam] Plate I.
40 CALIFORNIA ACADEMY OF SCIENCES
EXPLANATION OF PLATE IL
Tlidliitto.savrvs (ilcrniidrar.
All fi(iinrK Ihrcr finirtliK luilxral ><rze.
Fig. Irt. Section a througli craniuiu of tyi)e sjiecinieii, posterior to superior nares. See PI. i,
figs. 1 and 2, section a.
Fig. Ih. Section /) through cranium of type specimen, anterior portion of superior narial region.
See PI. I, figs. 1 and 2, section h.
Fig. If. Section r through craniinn of type specimen, middle rostral region. See PL I, figs. 1
and 2, section r.
Fig. 2a. Right quadrate, inner side.
Fig. 2/>. Right quadrate, outer side.
Fig. 3. Posterior end of premaxillary. T. alcrandrac {'!)
Fig. 4. Fragment of cpiadrate and temporal region of type sj)ecimen.
Legend.
i1/, maxillary /V, palatine
Pm, premaxillary L, prevomer
A^ nasal ' T. tooth
7'', frontal <^. quadrate
/'/', jircfrontal Sij. .s<iuamosal
A, doiditful elenient anterior to
narial oneninsjr
Memoirs CalAcadSci.VdlV
[MerriamI Plate II.
la
lb
2a
2b
42 CALIFORNIA ACADEMY OF SCIEN(JES
EXPLANATION OF PLATE LIL
Thalattosmtrus shastensia.
All pijnrrx three fourths imtural size.
Fig. L Superior view of craniiini.
Fig. 2. Lateral view of craniiim and luaiulihle.
Fig. 3. Lateral view of skull from right side.
Legend.
osai
te
M, maxillary ^'j, squanio
Pin, preniaxillary Q, quadrate
N, nasal Ep, epipterygoid (?)
F, frontal /'', i)alatine
Pr, parietal 1', prevomer
Pn, pineal foramen Ar, articular (?)
Pf, prefrontal -4«, angular
Pto, post-fronto-orl)ita1 '"^n, supra-angular
Ptg, groove for post-fronto-orliital D, dentary
,/, jugal !^p, splenial
Sc, sclerotie j>lates
Memoirs CalAcad SciYdlV
[Merfuam] Plate III.
44 CALIFOKNIA ACADEMY OF SCIENCES
EXPLANATION OF PLATK IV.
Fig. 1. Anterior jaw tooth associated with type specimen of T. nlcm)idr<ic. X 14.
Fig. 2«. ThalaUnnanrus shastensis. Inner side of right half of cranium and mandilile. Type
specimen. X |.
Fig. 2h. Tootli associated witli skull of T. sliastcnds shown in fig. 2a. X 2.
Fig. 2c. Tooth associated with skull of T. ffhastfinsis shown in fig. 2a. X 2.
Fig. 3. Thalattosaurua perrini. Inner side of right half of cranium and mandihle. Type
specimen. x |.
Fig. 4a. Nectosaunis haliiis. Superior aspect of fragment of cranium. Type specimen. X f.
Fig. 4Ji. N. haliv.<i. Inner side of right ramus of inandil)le. Type specimen. X ^
Fig. 4c. N. haliii.s. Outer side of middle portion of k'ft ramus of mandilile. Tyiie specimen. X |.
Fig. 5. N. halivs. (Xiter side of right ramus of mandihle. X |. The anterior end of the supra-
angular has l.)een weathered through.
Legend.
/), dentary Sc, sclerotic plate
C, coronoid /, jugal
An, angular Pr, parietal
Sa, supra-angvriar Sq, squamosal
Ar, articular Q, quadrate
Sp, splenial jl/, maxillary
/•', frontal PI, jialatine
I'f. prefrontal ", iirefrontal (?)
/'/(). post-fronto-orhital /', frontal (?)
Memoirs CalAcad^SciYdlV
[Merriam] Plate IV
2a
2b
4a
M
4b
46 CALIFORNIA Af'Al^EMA' OF SCIENCES
EXPLANATION OF PLATE V.
Fig. 1(7. ThahtUmtauruit nlexandrne. Pterygoid, lateral view. Type specimen. Natural size.
Fig. 1/*. Upper side of specimen shown in fig. la. Natural size.
Fig. Ic. Lower side of specimen shown in tig. hi. Natural size.
Fig. 2(7. Thalattosaitrus alexandrae. Lower side of prevomer. X -|.
Fig. 2b. Lateral view of specimen shown in fig. 2n. x |.
Fig. 3. Thalattosaurus perrini. Lateral view of prevomer. Median pair of teeth partly
restored. Type specimen, x |.
Fig. 4. Nectosaurus halius ('?) Pterygoid or jialatine, superior view. X H.
Fig. 5. Thalattosaurus, sp. Vomerine tooth. X H.
Fig. 6. Nectosniirvs haJivs (?) Maxillary. Natural size.
Memoirs CalAcad SciVdlV
[Merriam] Plate V
la.
lb
i^Mi,
2h
48
CALIFORNIA ACADEMY OK SCIENCES
Fig. 1. Lateral view.
Fig. 2. Superior view.
EXPLANATION OF PLATE VL
ThaJdltoMmrvd olernndritr.
Reconstruction of the skull.
Ahnvt nne lidlf natiinil size.
The temporal and fronto-parietal regions and a portion of the mandible are restored from
T. shnstensis.
Legend.
Pm, premaxillary
M, maxillary
iV, nasal
F, frontal
Pr, parietal
Pn, pineal foramen
Pf, prefrontal
Pfo, post-fronto-orbital
J, jugal
L, lachrymal
PI, palatine
iS'c, sclerotic ring
Sq, squamosal
Q, (juadrate
Ar, articular
iS^rt, supra-angular
.47), angular
D, dentarv
Memoirs CalAcad.Sci.VdlV
[Merriam] Plate VI.
50 CALIFOKNIA ACADEMY OF SCIENCES
EXPLANATION OF PLATE VII.
All f(iures three ftnirtha natural size.
Fig. 1. Thahittosaiirns alexandrae. Anterior dorsal vertebra, side view.
Fig. 2. T. alexandrae. Dorsal vertebra, anterior side.
Fig. 3. T. alexandrae. Anterior caudal vertebra, side view and sagittal section. Tbe neural
spine appears to be somewhat too erect in the figure. Type specimen.
Fig. 4. T. shaMensis. Neural arch of a cervical or anterior dorsal vertebra. Type specimen.
Fig. 5. Neetosaurii.'! halivs. Weathered cross-section of vertelira. Type specimen.
Fig. 6. Thalattosaunis ])errini. Anterior dorsal rili. Type specimen.
Fig. 7. T. shastensis. Head of dorsal rib. Type specimen.
Fig. 8. T. alexandrae. Pubis (?)
Fig. 9. T. alexandrae. Ischium (?) Type specimen.
Fig. 10. T. alexandrae. Pubis (?)
Memoirs CalAcad.Sci.VdlV
[Merriam] Plate Vll,
10
52 CALIFOUNIA ACADEMY OF SCIENCES
EXPLANATION OF PLATE VIII.
,4/? fgu'irx 111 ire fourths luitiirnl size.
Fig. 1. Thalattosnvriis alexdiidrae. Coracoid. Type specimen.
Fig. 2. T. alc'xandrae. Scapula. Type specimen.
Fig. 3. T. shastensis. Scapula. Type specimen.
Fig. in. T. nlexandrae. Left humerus, superior view.
Fig. 4?). Inferior view of specimen shown in fig. 4r7.
Fig. 6. T. alexandrae. Radius.
Fig. 6. T. alexandrae. Ulna. Type specimen.
Fig. 7. T. shastensis. Ulna. Type specimen.
Fig. 8. T. sliastensitf. Humerus. Type specimen.
Memoirs CalAcad SciX'dlV
[Merriam] Plate VIII.
4a
4b
MEMOIRS OF THE ACADEMY.
(Quarto)
VoU'MK 1.
No. 1 — A Catalogui-' of tlu' Sperii'S of Mossi'S found up t(i the present time on tlie North-
West Coast i)f the United States, and esi)eeially in California. By r,eo I.es-
quereux .tli.OO
No. '2 — Principles of the Natural Systenj of ^'ld(•anie Rocks. By F. Baron Riclith<ifeu
(out of print).
VoU'MK II.
No. 1 — On the Anatomy of Sutroa rostrata, a New Annelid of thr Suli-family TyUiidivi-
culina. By Gust a v Eisen .7")
No. 2 — On some Aneient Seulpturrs fnuii the Pacific Slope tif (inateniala. HyOustav
Eisen 1.00
No. 3 — On California Eudrilida\ By Gustav Eisen 2. 00
No. 4 — Pacific Coast Oligochteta. 1. By Gustav Eisen 2.50
No. 5 — Pacific Coast Oligochfeta. II. By Gustav Eisen 2.50
VOLDIK III.
The Paleontology and Stratigraphy of the Marine Plioci'ue and Pleistocene of San Pecho,
California. By Ralph Arnold 8.50
Volume IV.
The Fishes of Pan^ania Bay. By Charles H. Gilbert and Edwin C. Starks :!.00
VOLUJIE V.
No. 1 — The Thalattosauria, a Grouj^ of Marine Reptiles from the Triassic of California.
Bv John C. Merriam .75
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